Question 1

Why 5 ft/s minimum?

Accepted Answer

Below 5 ft/s, biofilm and fine sediment stay attached. At ≥5 ft/s the shear stress mobilizes loose material so the hydrant can carry it out.

Question 2

How much water does flushing waste?

Accepted Answer

Depends on main size. A 4-hour 1,000-gpm run consumes 240,000 gallons — but it's a small fraction of annual production and protects water quality.

Question 3

What is unidirectional flushing (UDF)?

Accepted Answer

Closing valves so flow goes one direction at scour velocity, isolating one main at a time. Uses far less water than conventional flushing and actually cleans pipe walls.

Question 4

When should I flush?

Accepted Answer

After main repairs, before bacteriological samples, when complaints spike, and at least annually system-wide. High-water-age areas may need quarterly flushing.

Hydrant Flushing Volume Calculator